Trapeziometacarpal prostheses and implants are designed to restore the strength and mobility of the anatomical joint of the thumb, between its metacarpal and the trapezium, when the joint is damaged by a degenerative or inflammatory pathological process. Many trapeziometacarpal prostheses are stem prostheses in which the metacarpal prosthetic component is anchored at one end in the metacarpal by an elongate stem while the other end of the prosthetic component is mounted pivotably either in a prosthetic component attached to the trapezium or in a cavity hollowed out in the trapezium. The implantation of these total or partial prostheses requires considerable cutting of the bone substance of the trapeziometacarpal joint and restores a ball-and-socket type of mobility which, from the point of view of kinematics, does not correspond to the mobility of the anatomical joint. Moreover, in the event of poor implantation, there are real risks of wear, luxation, or even prosthesis fracture. Some trapeziometacarpal implants without stems have also been proposed, those implants being implanted into a cavity or cavities formed in the trapezium and/or metacarpal. Often times, because of the compressive stresses applied to the implant body by the surrounding ligaments of the joint, the implant body gradually engages deeper in the bones, reducing the space between the bones and, consequently, their relative mobility.
Total trapeziectomy may be performed based on indications of, for example, peritrapezial arthritis, that is, arthritis affecting the different joint surfaces of the trapezium, and isolated arthritis, such as arthritis of the trapeziometacarpal joint, also called rhizarthrosis. Trapeziectomy allows the first metacarpal to articulate in the space that was previously occupied by the trapezium. However, if no movement is associated therewith (e.g. the muscles are weakened or not able to provide sufficient forces), the column of the palm of the hand retracts due to ligament tension. As such, the ligament tension collapses the space that was previously occupied by the trapezium, prevents articulation of the first metacarpal, and causes pain due to secondary arthritis. As such, the total trapeziectomy is typically only employed together with ligamentoplasty. That is, a structure that is formed from, for example, a ligament taken from the patient or synthetic fibers is implanted in the space that was previously occupied by the trapezium to inhibit the base of the thumb from descending. However, the results of such ligamentoplasties are typically poor. In particular, such ligamentoplasties are typically associated with a very long functional recovery period, awkward shortening of the column of the thumb with hyperextension compensating the metacarpophalangeal joint, decreased gripping strength of the thumb, and long-term deterioration of the structure due to a metacarpotrapezial and/or metacarpal scaphoid conflict, which is in turn due to the shortening of the trapezium cavity.
Previously, trapezium interposition implants were proposed to address the issues described above. Some trapezium implants typically include a single-piece silicon body having a cylindrical part to replace the trapezium, a concave end to engage the scaphoid, and an opposite end having a conical stabilizing tail to be inserted into the metacarpal. Unfortunately, these interposition implants typically cause one or more problems, such as silicon debris causing “siliconites” with significant bone resorption, implant fracture, and/or implant instability.
Other trapezium implants are designed to replicate the natural trapezium bone. However, these implants also cause one or more problems. For example, when a trapeziectomy is performed, arthritis has typically advanced to a degree that the tissues surrounding the trapezium are significantly deformed. As such, it may be difficult to stably position such implants. Furthermore, if stabilizing means are attached to these implants, they are particularly painful for patients due to the excess stresses they cause in the hand.
Another type of trapezium interposition implant includes a spherical or ellipsoid single-piece body that is placed in the trapezium cavity. This implant addressed the issues of retraction of the column of the thumb and the recovery period related for trapeziectomy. However, given its convex shape, this implant must be placed using a delicate surgical technique based on medialization of the implant. Specifically, the implant must be pushed into a “cul-de-sac” prepared by the surgeon by partial resection of the trapezoid facilitate implant stability.